For Mac users, unknown artist and albums, duplicate songs and missing artwork -- if these describe on your iTunes music library, you can try this Tunes Cleaner for Mac to fix all of them. It's described as the most practical and easiest-to-use iTunes cleaner program to clean up iTunes music library.
Tunes Cleaner for Mac
> Get album artwork for iTunes music library
> Clean up iTunes and external music folders smartly
> One-click to delete duplicates in iTunes music libraries
> Clean up iTunes music library and apply to iTunes in one click